MICROWAVE DETECTION USING GAAS ALAS TUNNEL STRUCTURES/

The Schottky diode has been the 'work-horse' device for microwave dete ction since the 1940s, but suffers from having a performance that is s trongly dependent upon temperature. We have therefore carried out a de tailed programme of research into microwave detection using GaAs/AlAs tunnel devices, in which electrical conduction is much less temperatur e-dependent than in Schottky diodes. A suitable structure for this kin d of device consists of one or more very thin AlAs layers (1 - 10nm) e mbedded in GaAs: such a structure can be easily made with modem semico nductor growth techniques. In this paper, we describe the design, grow th, fabrication, and assessment of such devices, and compare their per formance with that of existing detectors. As expected, the tunnel devi ces have a weaker temperature-dependence. Additionally, they have a nu mber of other advantages such as a low noise-temperature ratio, flexib ility of design, and the ability to work without external bias. We con clude by discussing how similar structures could be used to realize ot her key components of a microwave system: mixers and sources.